In accordance with popularization of information terminals, the needs for a flat panel display as a display of a computer have been increasing. Further, in accordance with development of information oriented society, since information conventionally provided on a paper medium has come to be provided as electronic data, the needs for electronic paper or digital paper as a mobile display medium, which is thin and light as well as is easily portable, are increasing. In view of such a background, development of a flat panel display device has come to be in progress.
Generally, in a flat panel display device, a display medium is formed by use of an element utilizing such as liquid crystal, organic EL and electrophoresis. Further, to assure display uniformity of an image plane and rewriting speed of an image plane, a technology utilizing an active operating element constituted of a thin layer transistor (hereinafter, being called as a TFT) has come to be a mainstream.
Herein, a TFT element is generally manufactured by successively forming a semiconductor layer primarily comprising such as a-Si (amorphous silicon) and p-Si (polysilicon) and metal layers of such as source, drain and gate electrodes on a glass substrate.
Conventionally, to form a bus line, an electrode pattern and a semiconductor layer on a substrate, patterning in a circuit form is generally performed by means of a photolithographic technology (hereinafter, being also referred to as a photolithographic method). A photolithographic technology is a method, in which after photosensitive resist is coated on a thin layer to be patterned, which is exposed through a photomask and developed, the exposed thin layer portion is subjected to patterning by dry etching or wet etching. And after patterning, unnecessary resist is peeled off and layer formation of the overlying materials is repeated to prepare a semiconductor material.
In this manner, a photolithographic method has been utilized for fabrication of a TFT element; however, there were problems that the manufacturing process is complex in addition to large scale equipment such as a clean room is necessary. In recent years, as a technology to compensate the demerit of a conventional manufacturing process of a TFT element utilizing a photolithographic process, extensive research and development on an organic TFT element, utilizing organic semiconductor materials, is in progress (refer to JP-A 10-190001 (hereinafter, JP-A refers to Japanese Laid-Open Patent Publication No.), and Advanced Material (Review) No.2, 99 (2002)).
A manufacturing method of an organic TFT depends on an element structure, however, for example, in the case of a (bottom gate)-(bottom contact) structure in which a gate electrode is formed on a substrate, after a gate electrode has been formed on a substrate by utilizing a photolithographic technology, a gate insulation layer is formed on the gate electrode employing a TEOS source by means of plasma CVD or a coated insulation material is formed by means of printing.
Then, a source electrode and a drain electrode are formed by utilizing a photolithographic technology, and thereafter, a pretreatment is performed to form an organic semiconductor layer on the channel portion between a source electrode and a drain electrode.
An organic semiconductor material includes a high polymer material and a low molecular weight material, and the methods to form an organic semiconductor portion thereof on a channel portion are different from each other.
A forming method for an organic semiconductor portion comprising a high polymer material includes a method in which a polymer material being dispersed in a solvent or a solution of a polymer material being dissolved is coated to form a layer.
On the other hand, as for an organic semiconductor material comprising a low molecular weight material, film formation is performed by means of evaporation under vacuum; however, layer formation by coating is also partly applied by selecting a solvent and a dissolution condition. A spin coat method and an inkjet method are utilized for the coating, and a micro contact printing method has been also studied.
After an organic semiconductor material comprising a polymer material or a low molecular weight material has been coated, the coated organic semiconductor material is dried to remove a solvent. As a drying method, a method to evaporate a solvent under vacuum or a method to heat the material on a hot plate is applied.
In an assembly process of a TFT panel, it is general to fix an alignment of liquid crystal molecules at the time of no application of electric voltage by forming an alignment layer on the plane of a TFT substrate, on which a formed TFT is arranged, and applying a rubbing treatment. In a forming process of an alignment layer, a polyimide solution is coated on a substrate by means of such as printing, inkjet and spraying, and the alignment layer is dried in a drying process.
In a drying process, when a long time is required to dry an alignment layer, there is caused a problem of uneven drying and uneven alignment layer thickness. Therefore, a method to blow gas, having a temperature necessary to evaporate the solvent of an alignment layer, against the surface of the alignment layer has been proposed (refer to JP-A Nos. 2003-57625 and 11-264978).
In the case that applying a drying process under vacuum to dry a coated semiconductor material after having been coated, a grate amount of time is necessary for the drying process, which is one of demerits of a coated semiconductor, resulting in a problem against manufacturing at a low cost without a vacuum process. Further, in the case of drying by heating a substrate on a hot plate, the way of heat conduction from the hot plate is not uniform resulting in uneven drying depending on the places on the substrate, whereby a problem of causing uneven characteristics among elements on a allay substrate.
On the other hand, in JP-A Nos. 2003-57625 and 11-264978, a method to dry an alignment layer coated on a substrate, on which a TFT is formed, in a short time is disclosed, however, a method to dry a semiconductor material to form a TFT is not disclosed; therefore these are not applicable for fabricating a TFT.